It has been suggested to use a wind turbine blade with an outer shape that may be changed during use. Particularly, it was disclosed in WO 02/051730 to provide a movable or deformable part of a wind turbine blade towards the root, where the chord length is largest. Hence the chord length of the widest part of the blade may be reduced in high winds so that the strain is reduced.
It has also been suggested to deform the leading edge and/or the trailing edge by bending the profile upwards or downwards. For example in WO 2004/088130 it was suggested to bend the leading edge zone and/or a trailing edge flap by means of a smart material or a hydraulic piston assembly. Part of the blade wall is made of a passive, flexible rubber, and during use the passive, flexible rubber is stretched to conform to the smart material or the hydraulic piston assembly. In one embodiment, the rubber comprises isolated voids.